Automatic headlight dimmer with antioscillation circuit



Dec. 15, 1959 J. RABINOW 2,917,664

AUTOMATIC HEADLIGHT 01mm wrm ANTI-OSCILLATION cmcurr Filed on. 14, 195::

Sensitivity INVENTOR JACOB RA B/NOW MZZ ATTORNEY United States PatentAUTOMATIC HEADLIGHT DIMMER WITH ANTI- OSCILLATION CIRCUIT Jacob Rabinow,Takoma Park, Md.

Application October 14, 1953, Serial No. 385,942

14 Claims. (Cl. 315-'83) This invention relates to-an improvedautoma'tic'headlight dimmer of the type utilizing a photosensitiveelement for detection of the: light conditions in advance of a vehicleand the dimming of Vehicle headlights in ac cordance with suchdetection.-

A primary object of the inventionis the'provision of means forminimizing the annoyance of headlight oscillationcaused by lightfrom'the' controlled vehicle being reflected back by roadside objects.This condition arises when the automatic dimmer on a vehicle isenergized by reflected lights from the vehicle headlights strikingagoo'dreflecting surface such as a bright road sign, direction'alwarning reflector, etc. The reflected light causes dimming of theheadlights, and very frequently the dimmed lights no longer strike thereflecting" surface with suflicient intensity to cause the automaticdimmer to remain actuated, and, as a result, the dimmer again raises theheadlights. Therefore the bright lights go' mechanical scanner, and thepresent invention provides a compact mechanical drumfor this purposewhich requires a minimum of space and is characterized by rugg'edness,simplicity and inexpensive c'onstructionl Still another object is theprovision" of a compact automatic dimmer control unit of exceedingly.compact design and inexpensive construction, which isre'ad'ily'accessible for repair or tube replacement;

The specific nature of the invention as well'a's other objects andadvantages will clearly; appear from a description of a preferrede'r'nbodiment'as shown in the ac-' companying drawing in which:

Fig. 1' is a circuit diagram of the invention;

Fig. 2 is a' sectional-view'taken on line 22of Fig. 3 of ac'ornpactas'sembly e'rnbodyingtlie invention but using a scanning druminstead of adisk; p

Fig. 3 is a sectional view"taken"online3 3"of'Fig. 2;

Fig. 4 is a similar sectional view of a modifiedconstruction wherein the1on8 iS replaced" a reflector; and

Fig; 5 is a raph showing the change in sensitivity due to ordinarydilflriiilfg and fo reflective dimming. v

Referring to Fig. 1, the li htfroth the field'ofview to the left of lens2, representinggeherally the same field as is" illuminated by thebrightbeams of the headlights, passes through'the lens and is focussedin the plane'of' a spirally perforated Nip'kow' disk 4continua'llydrivenb'y a small motor 6 from a suitable supply source, which may bethe standard automobile battery and generator system. AS ther'not'or 2does no other work thallio 10' tifo the scanningdisk 4} it fiiay li'o"Small; Motors 2,917,664 Patented Dec. 15, 1959 no greater than an inchin their largest dimension are available for this purpose, and may beeither the usual D.-C. motors or A.-C. motors of the type used to driveelectric clocks, in which latter case the motor may be driven by thestandard vibrating power supply used with automotive electronicequipment such as automobile radios, and which is also the type of powersupply that would normally be used with the electronic circuit'shown inFig. 1. Since the power supply is-conventional, and its design for anyspecific circuit is a matter within-the skill of any electronics circuitdesigner, it is not shown.

It will be seen that an image of the field of-view is formed on thesurface of the scanning element 4, and'the' light from a portion of thisimage will be admitted through that perforation 8 which happens to becrossing the image at that point, as described in.my prior patent, No.2,632,040. Light which passes through the perforation will, if it is ofsufficient intensity, actuate the photw cell 10, producing an outputsignalon lead 11, which is amplified by amplifier 12 which will now bedescribed.

The signal on lead 11' is fed to the grid of tube 13 which is operatedas a cathode follower to produce an amplified power output at itscathode 13a. This is fedto apeak-to-pe'ak rectifier arrangementcomprising diodes 17 and 14, and capacitors 19 and 15. The constants ofthe peak detector are so selected that the variations in light intensityof the normal background field of view when there is no headlight orother brightsource of illumination'present will not produce sufficientoutput at the grid'21 of amplifier tube 1.8 to deenergize the relay 20.The amplifier described has been found very satisfactory, but it will.be understood that any suitable amplifier' circuit may be used toprovide a signal of suflicient intensity to the detector, and likewise,any suitable known signal detecting circuit may be used in place of thatshown.

The light of the oncoming headlight is so much moreintense than thegeneral background that when such a great amount of light passes througha scanning aperture of disc 4, a very high peaksignal results, ofsuflicient intensity to release relay 20'.

Release of the relay 20 moves both of its switches over from theposition shown to the opposite position. Switch. 22 in' the positionshown closes contact 24 to complete a circuit from battery 26, throughfootswitch 28 which is shown in the beam-up or Bright position throughswitch 22 and contact 24 to the bright circuit of the headlight.Uponrelea'se of relay 20 by a light in the field of. View, switch 22engages contact 30' which disconnects the bright circuit and closes thedim circuit of the headlights, thus dimming them as required. At thesame time, switch 32 of the relay changes from its Bright position toits Dim position. In the Bright position (shown in Fig. 1), switch 32completed a circuit from potential divider 34through switch 32, throughresistance 36 to ground This established a certain biasing potential, onthe grid 21 of tube 18 which determined. the sensitivity of the systemat a predetermined level. In the Dim position of switch 32, the circuitfrom potentiometer device 34 is opened, and the included partof 34 actsthen only as a resistor between the grid'21- and the divider 40, so thatthe full potential from divider- 40 is now'impressed on the grid 21,increasing the sensi tivity of the system by a suflicient factor so thatevenif the oncoming carimmediately dims its lights, the reducedintensity of its beam is compensated by the increasedsensitivity and therelay 20 remains released.

If the signal which initiated the above describedaction came not fromanother headlight, but was a reflection of the cars' own headlights,upon the occurrence of' dimming as described above, the reflection maygreatly diminish'and the lights would, inmy prior system and" in otherheadlight systems, rapidly oscillate between the bright and dimpositions, producing an objectionable blinking. I therefore provide acondenser 42 across re sistance 36. It will be noted that in the Dimposition switch 32 has not only disconnected potential divider 3d fromground, but has also connected resistance 36 and condenser 42 throughcontact 44 and resistance 46 to the B-}- supply, thus putting the B-}-across condenser 42 (swltch 48 being open as shown). Now, when the relaycircuit is reenergized and resumes the initial bright position as shownin Fig. l, the positive charge on the condenser opposes the potentialdrop which would otherwise occur through divider 34 and resistor 36, anduntil the condenser is discharged through resistor 36 and the grid 21circuit, the relay remains energized and the beam remains Bright eventhough the photocell is being energized by a light. This continues untilthe condenser is sufliciently discharged so that normal operation isresumed. If the time constant of the R-C combination 36, 42 is madesufliciently great, a delay in the order of 1 /2 seconds can easily beprovided, which I have found to be satisfactory for the purpose.

The operation accomplished by the above described circuit elements is asfollows: When the lights are dimmed by a reflection, they go downpromptly and as the reflected light is no longer seen by the photocell,relay 20 is reenergized promptly and the lights return quickly tobright. Now, for approximately 1 /2 seconds depending on the timeconstant of 36, 42 the lights stay bright even though the reflectedlight again causes a signal output to be produced by the amplifier, thenthere is another brief down flick and the same operation is repeated.Thus, even if the vehicle is not moving and its lights shine directlyinto a reflector, there is only a brief down flick for, say, of a secondthen the lights stay up for 1 /2 seconds, then another down flick for /5second and up for 1 /2 seconds, etc. The road ahead remains illumin atedfor approximately 90% of the time, which is deslrable, and the downflicks are so brief in duration as to be quite unobjectionable to mostpeople. If the car is in motion as is normally the case, by the time oneor two flicks have occurred, the reflector has been passed. If anothercar comes in sight of the photo-multiplier cell at this time and issufliciently far away, the sensitivity of the system may be sufficientlyreduced for a fraction of a second so that dimming would be delayed, butsince the system need be set so as to be less sensitive only to therelatively weak reflected signal to accomplish the above anti-reflectionaction, a bright headlight, such as is due to a car rounding a curve ortopping a hill nearby, V

will overcome the slight inhibiting potential due to condenser 42 andcause immediate dimming in any case. Furthermore, as the decay of thecondenser is logarithmetic, its initial decay is quite rapid, so thatthe maximum loss of sensitivity is only for a fraction of a second,durlng which time a distant vehicle is relatively little annoyed by thebright headlights. In practice, this system can be readily adjusted sothat a very satisfactory compromise between the reduced sensitivity tooncoming cars and good antireflection action is achieved.

One objection to the above described system is that if the dimming isdue not to a reflection, but to an oncoming vehicle, as soon as thatvehicle is passed there is a short period of low sensitivity, due to theabove described action of condenser 42. This I eliminate by providingadditional means whereby condenser 42 is effective only if the downflick is of short duration, as happens when it is caused by areflection, but not when the down beam remains down for a substantialperiod, as is normally the case when the relay 2!) has been actuated bythe lights of an oncoming vehicle. For this purpose 1 provide a secondrelay 50 which is actuated by the dimming switch 22 when it engagescontact 30 to dim the headlight. Relay 50 is shunted by a condenser'52,, and a series resistor 54 is added to provide a delay action.

After a predetermined delay (approximately /5 second), relay 50 closesswitch 48 to short the condenser 42 through a low resistance 56, whichis provided to prevent arcing of the contacts of switch 48. It will beseen that relay 50 has no effect on the action of condenser 42 if theheadlights are dimmed by reflection, because in that event, as soon asthe lights dim, there is no longer a reflection and relay 20 isimmediately reenergized so that there is only a brief down flick whichdoes not give the second relay 50 time to close its contacts, due to thetime delay of the R-C combination 52, 54. Thus, the R-C combination 36,42 is effective to produce the antireflection action previouslydescribed. On the other hand, if the dimming is due to an oncomingheadlight, the dim beam is practically always maintained for at least asec end, which gives relay 50 time to close switch 48 and inhibit thedelay action of R-C combination 36, 42. Thus, as soon as the oncomingvehicle is passed, the system is immediately at full sensitivity andready to operate normally if another vehicle should at this momentappear. The action is shown by the graph of Fig. 5, where the ordinatesrepresent sensitivity and the abscissae represent time. The initialcondition (stage A) is shown in Fig. 1, with the beam bright and thesensitivity therefore low, as previously explained. In stage B, anoncoming headlight is detected and the beam dims, while the sensi tivityis increased. In stage C, the oncoming headlight is passed and the beamagain brightens. In stage D, a reflection is seen and the beam dims,then immediately comes up again as the reflection is lost; however, atthis time the sensitivity does not go back to its initial level C asbefore, but due to the action of 36, 42 goes down to a lower level thanoriginally, and gradually resumes its original sensitivity as condenser42 discharges. During the first part of stage E, it will thereforerequire a stronger signal than normal to cause dimming. This can beprovided by an oncoming headlight at a reduced dis tance, but not by therelatively weak reflection. The times when reflection causes dimming arenormally quite infrequent as normal reflectors on the side of the roadcan be avoided by the directivity of lens 2, and it is only when theroad curves to the left, or at a dead-end sign, or some similarcondition, that reflection will occur at all; and since the times whenan oncoming headlight will appear in the field of view immediately aftera stage E type of action are still less frequent, it will be evidentthat this represents a relatively rare condition, and even then, if theoncoming headlight is close, when immediate dimming is important, suchimmediate dimming will occur due to the strong signal received from thenearby headlight.

In practice, the above action has been found to produce a verysatisfactory solution to the problem.

Instead of the R-C type delay shown at 52, 54, any known type of slowacting relay could, of course, be employed, such as a relay providedwith a copper slug, or a dashpot or other mechanical type delay could beused.

While I have shown the above anti-reflection circuit in connection witha scanning-type dimmer such as is discussed in my prior patent, it willbe evident that it is by no means restricted to this type of automaticdimmer, but will be equally effective in conjunction with anyconventional type of automatic dimmer using a photosensitive element toactuate a relay through an amplifier, as the R-C delay caused by 36, 42could be applied to the grid of a suitable stage of the amplifier tocause the above described action no matter what type of automaticdimming circuit is used. It will also be apparent that instead of an R-Cdelay an R-L delay, thermal delay or mechanical delay could be used incarrying out the principle which is illustrated by the above circuit,which is shown by way of example only.

It often occurs that the driver of the oncoming vehicle if he does nothave an automatic headlight dimmer but relies upon. old-fashioned footdimming will fail to re:

spend; to; the automatic dimming by also dimming his lights. In that.case, it is customary'to call his attention to. his neglect by blinkingones own lights. I provide for this situation and alsofor overriding theautomatic control by means of switch 61 which is the usual foot switchactuated by a fioorboard'button 60 so that each time-button 60 isdepressed, switch 28 changes from its current position; to'the oppositeone, as is well known. Thus, if the beam is bright, as shown in Fig. l,and the floor switch is pressed, the beam will be depressed to dimposition and stay down regardless of the automatic system, ascurrentwill flow directly from battery 26 through switch 28 to the dimmingcircuit. When it is desired to resume automatic operation, the footswitch is again depressed.

1;. provide a spring-opened switch 62 over and out of contact. with footswitch 60. If headlights have been automatically dimmed, and switch 62is lightly touched with the foot, the'plate of tube 18is groundedthrough resistance 64-, and switch 62, directly through the metal button60 to cause relay to be energized and the lights to return to brightas'long as switch 62 is grounded. Thus, by lightly tapping switch 62 afew times, the lights will be made to blink to'remindthe'oncoming driverto dim his lights. However, if the foot button is heavily pressed,switch 28- will be actuated to dim position regardless of the automaticsystem-as above explained. It will thus be seen that the operator hasfull control and can at will put the automatic system into operation,overrideitto fixed dim position which he may be required. todo by law incity driving or in some tunnels or cause the beam to temporarily bebright regardless of conditions ahead.

Instead of contacting the button 60, it will be apparent that switch 61could be grounded on any convenient spring-mounted ground contact, andinstead of being directly over: button 60, it need only be sufficientlyclose to the button sothat the operators foot covers both switch 62 andbutton 60, so that a light foot pressure will first ground switch 62 andcontinued foot pressure will then operate button 60. However, by placingswitch 62 over the'button', there is" no chance of missing one andhitting the other'when feeling for these switches with the foot. Sinceswitch62 isat a fairly high voltage, it should, of course, be wellinsulated.

Referring now to Figs. 2 and 3, the entire assembly ofcomponentsshown'in Fig; 1' can be compactly housed in" a smallcasing 70.The physical elements which must be housedin'the' casing comprise asingle photo-multiplier cell 10 and a scanning drum 74 which surroundsthe light-sensitive end of the tube and is provided with scanningapertures 76 so spaced in a helical-band around the drum 74 that as thedrum is rotated at least a single aperture is at all times crossing thewindow of the photo multiplier cell, and as all the successive apertures76 traverse the window on each revolution of the drum, the entire areaof the window is scanned for each revolution of the drum. Motor 6 drivesthe drum by means of a belt 78 which fits an annular grooved portion 80on the drum. The drum is provided with a rigid shaft 82 coaxialtherewith which is supported for rotation by any suitable bearing 84,such .as an Oilite bearing, or small ball bearings may be used. Theapertures 76 may be circular as shown, or may be square or even in somecases in the form of narrow slits, the essential thing being that asmall area of the image is observed through the aperture at any onetime.

Lens 2 is mounted in the front of the casing 70. A light shield 86 maybe provided if desired to define the desired field of view. The interiorof the casing and all components should be coated with darknon-refiecting paint to prevent optical interference with the desiredlight signals. Due to the curvature of the drum, its surface will notcoincide exactly with the focal plane of the lens, but with suitablychosen dimensions this effect is negligible for practical purposes,asathe circumferential.

extent of the image is in the order of A- inch and the a-p proximationto a straight line of thisfshort circumferential distance is adequatefor practical purposes.-

The remaining space in the casing is used to house the other circuitcomponents of Fig. 1, except, of course, fon the battery, power supply,and floor switch.

Tubes 13 and 18 may be housed in a'single envelopeas a dual tube, andsimilarly the two diodes may be a dual tube as shown, or may be singlediodes. The remaining circuit elements should be selected for reasonablysmall dimensions and can easily be housed in a very small space.

Fig. 4 shows a casing similar to Figs. 2 and 3'exceptthat the lens isreplaced by a reflecting surfac'e 90 so shaped as to cause the lightbeam presenting, the field-of. view to focus at the same area on thesurface of-drum 74' as: before in the case of drum 74. A glasswindow 92may be provided to exclude dirt andmoisture, or the aperture may bemounted against the windshield of acar in a corner where it does notinterfere with the driver s' vision but is cleaned by the windshieldwiper. The powersupply (not shown) is preferably. housed in a separateunit for convenient placement in any suitable location and is connectedby leads to the dimmer circuit.

One particular advantage ofthe drum shown in Figs. 2, 3 and 4 is that itmay be made of magnetically permeable material and thus. serve as amagnetic shield. for the photo-multiplier cell. Such cells are highlysusceptible to'the disturbing influence of magnetic fields and theproximity of the motor may introduce such a field,- which mightotherwise require carefulrnagnetic shielding, but the drum may bemadetoserve this function very efficiently due to its construction as alight shield.

While the main relay 20' has been shown as normally energized, beingdeenergized by the effect of a light signal, it will be obvious thatthis relay could be normally deenergized instead in which case a lightsignal would cause the relay to become energized; in this case thecircuit including the peak detector would, of course, be reversed orinverted from the arrangement shown, but as the necessary changes areWithin the skill of any circuit designer, itis not considered necessaryto specifically show them;

It will be apparent that the embodimentsshown are only exemplary andthat various modifications can be made in construction and arrangementwithin the scope of my invention as defined in the appended claims.

I claim:

1. In a headlight dimmer, sensing means to detect light in a selectedfield of view, said sensing means cooperatively arranged with headlightdimming means to dim the headlights of a vehicle when said light exceedsa predetermined first value, means to brighten the lights when saidlight decreases below a second predetermined value, and desensitizingmeans to reduce the sensitivity of said dimming means for a short periodof time immediately following the brightening of the lights whereby thedimmer is made responsive only to light of a higher intensity than athird predetermined value higher than the said first value for the saidshort period.

2. An automatic headlight dimmer comprising headlights having a brightand a dim condition, a light sensitive element, means associatedtherewith for producing an electrical output related to the intensity ofa light signal affecting said element, a headlight dimming circuitactuated by said output to produce said dim condition of the headlightswhen said light signal exceeds a predetermined first value, means forrestoring said headlights to the bright condition when said light signaldecreases below a second predetermined value, and a desensitizing meansoperative to reduce the sensitivity of the dimming circuit for a shortperiod of time imme diately following the resumption of bright conditionof the headlights, whereby the dimmer is made responsive during saidshort period only to alight signal of a level higher than a thirdpredetermined value, said third value being higher than said firstvalue.

3. The invention according to claim 2, and further means arranged torender ineffective said desensitizing means when the time intervalbetween the dimming action and the subsequent brightening action isgreater than a predetermined duration.

4. The invention according to claim 3 and further means arranged torender inoperative said desensitizing means after the duration of saidshort period of time.

5. An automobile headlight dimmer comprising a light sensitive element,circuit means associated therewith for producing an electric outputrelated to the intensity of a light signal affecting said element, aheadlight dimming circuit electrically biased to a normal level ofsensitivity and actuated by said output to cause headlight dimming whensaid intensity is greater than a definite value and to discontinue saiddimming when the intensity of the light signal is reduced below adefinite level, means for increasing the sensitivity of the systemduring dimming and desensitizing means actuated for a definite shorttime period immediately after discontinuance of said dimming to changethe electrical bias of said dimming circuit to reduce the senstivity ofsaid system to a light signal.

6. The invention according to claim 5, said last means comprising timedelay means effective for said definite short period, said dimmingcircuit comprising a dimmer relay having a first position correspondingto bright headlight condition and a second position corresponding to dimheadlight condition, means connecting said time delay means into saiddimming circuit in said first position of the relay, and bias changingmeans under control of said time delay means to reduce the sensitivityof said system to a light signal while said time delay means isefiective.

7. The invention according to claim 6, said time delay means comprisinga condenser-resistor circuit having a time constant corresponding to thedefinite short period, means for charging said condenser-resistorcircuit in the second position of said relay, and means for connectingsaid charged condenser to said dimming circuit to produce said biaschange in the first position of said relay.

8. The invention according to claim 7, and means for renderingineffective said desensitizing means at a definite short time periodsubsequent to dimming, whereby said desensitizing action occurs onlywhen said dimming is of brief duration.

9. The invention according to claim 8, said last means comprising meansfor discharging said condenser in the second position of said relay, andfurther time delay means for delaying the operation of said dischargingmeans for a definite short period after the relay changes from the firstto the second position.

10. An automatic headlight dimmer comprising a lightconcentrating devicearranged in concentrate light from a field of view in advance of avehicle, a photo-sensitive electric cell having a photo-sensitivesurface near the focus of said light-concentrating device so that lightfrom said field of view is concentrated upon said surface, saidphotocell having a cylindrical exterior configuration, a cylindricalscanning drum mounted coaxially with said photocell for rotationthereabout, and having scanning apertures arranged to successivelytraverse contiguous portions of said surface as said drum is rotated;means for rotating said drum; and automatic headlight dimming meansactuated by the response of said photo-sensitive cell to light from saidfield of view which passes through said apertures.

11. The invention according to claim 10 and a housin enclosing saidphoto-sensitive cell, drum and driving means, said light-condensingdevice being a lens mountcd in said housing.

12. The invention according to claim 10, said lightconcentrating devicebeing formed by a reflecting surface of said housing.

13. The invention according to claim 10, and a peak detector responsiveto the output of said photo-sensitive device, said automatic headlightdimmer being controlled by the output of said peak detector.

14. The invention according to claim 13, and a cathode follower betweensaid photo-sensitive device and said peak detector.

References Cited in the file of this patent UNITED STATES PATENTS2,558,969 LeCroy July 3, 1951 2,560,748 Silva July 17, 1951 2,573,627Vanderlip Oct. 30, 1951 2,598,420 Onksen May 27, 1952 2,614,227Bordewieck Oct. 14, 1952 2,615,079 Pardue et al. Oct. 21, 1952 2,632,040Rabinow Mar. 17, 1953 2,687,337 Alford Aug. 24, 1954 2,707,524-Montgomery May 3, 1955 2,730,654 Rabinow Jan. 10, 1956

